We are getting an error connecting to HMRC MTD for the last 2 weeks with this error code CLIENT_OR_AGENT_NOT_AUTHORISED

We have tried all steps in help (switching of MTD and back on etc.) and can find no way of re-authorising the connection.  We have used MTD successfully for a long time and all the VAT details are correct. Logging on to HMRC also has no help on this issue.  Please can you help?!